Flipped the include guard and the pragma, and don't use the pragma for early...

Flipped the include guard and the pragma, and don't use the pragma for early versions of gcc (< 3.4)

src/regeximpl.h

-#pragma once
-
 #ifndef REGEXIMPL_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define REGEXIMPL_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 
 #include "stream.h"
 #include "stringsource.h"

src/scalar.h

-#pragma once
-
 #ifndef SCALAR_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define SCALAR_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 
 #include "content.h"
 #include <string>

src/scanner.h

-#pragma once
-
 #ifndef SCANNER_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define SCANNER_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 
 #include <ios>
 #include <string>

src/scanscalar.h

-#pragma once
-
 #ifndef SCANSCALAR_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define SCANSCALAR_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 
 #include <string>
 #include "regex.h"

src/scantag.h

-#pragma once
-
 #ifndef SCANTAG_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define SCANTAG_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 
 #include <string>
 #include "stream.h"

src/sequence.h

-#pragma once
-
 #ifndef SEQUENCE_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define SEQUENCE_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 
 #include "content.h"
 #include <vector>

src/setting.h

-#pragma once
-
 #ifndef SETTING_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define SETTING_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 
 #include <memory>
 #include <vector>

src/singledocparser.h

-#pragma once
-
 #ifndef SINGLEDOCPARSER_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define SINGLEDOCPARSER_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 
 #include "yaml-cpp/anchor.h"
 #include "yaml-cpp/noncopyable.h"

src/stream.h

-#pragma once
-
 #ifndef STREAM_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define STREAM_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 
 #include "yaml-cpp/noncopyable.h"
 #include "yaml-cpp/mark.h"

src/streamcharsource.h

-#pragma once
-
 #ifndef STREAMCHARSOURCE_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define STREAMCHARSOURCE_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 
 #include "yaml-cpp/noncopyable.h"
 #include <cstddef>

src/stringsource.h

-#pragma once
-
 #ifndef STRINGSOURCE_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define STRINGSOURCE_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 
 #include <cstddef>
 

src/tag.h

-#pragma once
-
 #ifndef TAG_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define TAG_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 #include <string>
 
 namespace YAML

src/token.h

-#pragma once
-
 #ifndef TOKEN_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define TOKEN_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 
 #include "yaml-cpp/mark.h"
 #include <iostream>

test/emittertests.h

-#pragma once
-
 #ifndef EMITTERTESTS_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define EMITTERTESTS_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 namespace Test {
 	bool RunEmitterTests();
 }

test/parsertests.h

-#pragma once
-
 #ifndef PARSERTESTS_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define PARSERTESTS_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 namespace Test {
 	bool RunParserTests();
 }

test/spectests.h

-#pragma once
-
 #ifndef SPECTESTS_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define SPECTESTS_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 namespace Test {
 	bool RunSpecTests();
 }

test/tests.h

-#pragma once
-
 #ifndef TESTS_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 #define TESTS_H_62B23520_7C8E_11DE_8A39_0800200C9A66
 
+#if !defined(__GNUC__) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) || (__GNUC__ >= 4) // GCC supports "pragma once" correctly since 3.4
+#pragma once
+#endif
+
 #include <string>
 
 namespace Test {